1. Field of the Invention
The instant invention relates to the treatment of acid mine drainage, consisting of a formulation whose main components are waste stream products that produce a feedstock that can be agglomerated into briquettes, blocks or pellets. This formulation creates a hybrid product that can be used in a variety of treatment applications (passive or active treatment) to neutralize acid mine drainage (AMD) in an effective and economical way.
2. Description of the Related Art
Acid mine drainage (AMD) forms when sulfide minerals in rocks are exposed to oxidizing conditions in coal and metal mining, highway construction, and other large-scale excavations. There are many types of sulfide minerals, but iron sulfides common in coal regions, pyrite and marcasite (FeS2), are the predominant AMD producers. Upon exposure to water and oxygen, pyritic minerals oxidize to form acidic, iron and sulfate-rich drainage. The drainage quality emanating from underground mines or backfills of surface mines is dependent on the acid-producing (sulfide) and alkaline (carbonate) minerals contained in the disturbed rock. In general, sulfide-rich and carbonate-poor materials are expected to produce acidic drainage. In contrast, alkaline-rich materials, even with significant sulfide concentrations, often produce alkaline conditions in water.
Acidity in AMD is comprised of mineral acidity (iron, aluminum, manganese, and other metals depending on the specific geologic setting and metal sulfide) and hydrogen ion acidity. Approximately 20,000 km of streams and rivers in the United States are degraded by AMD. Water treatment methods used to eliminate or reduce acidity and heavy metals precipitation from impacted waters can be grouped into two types.
One method is called active treatment. Active treatment involves neutralizing acid-polluted waters with alkaline chemicals. However, the chemicals are expensive, hazardous and the treatment facility is expensive to construct and operate. Six primary chemicals have been used to treat AMD including limestone, hydrated lime, pebble quicklime, soda ash, caustic soda, and ammonia. Each chemical has characteristics that make it more or less appropriate for a specific condition. The best choice among alternatives depends on both technical and economic factors.
The second method is called passive treatment. This technology involves the construction of a treatment system that employs naturally occurring chemical and biological reactions that aid Acid Mine Drainage (AMD) treatment and require little maintenance. Passive control measures include anoxic drains, limestone rock channels, alkaline recharge of groundwater, and diversion of drainage through man-made wetlands or other settling structures. The initial cost of building a passive systems are high, but the long term maintenance of the system are low relative to an active system.
There is a need for a product that incorporates the positive aspects of multiple materials, while minimizing or eliminating the negative properties. Since each AMD situation is different and the treatments are so variable, as follows, this product has been designed to be a hybrid product utilizing a neutralizer and binder component such as steel slag; a dissolution control and filtration component such as an organic material; optionally an oxidizing agent such as calcium peroxide, and a dispersant and neutralizer such as a surfactant. This results in a product allowing for the recycling of waste stream products in an effective, low-cost manner.